The invention relates to an optical reading device for reading information recorded in a track of an optical record carrier, which device comprises a radiation source for generating a radiation beam; an optical system for directing the radiation beam via the track onto a radiation-sensitive detector, the radiation beam producing a scanning spot on the record carrier; a driving device for displacing the scanning spot with respect to the record carrier in a longitudinal direction of the track at a given scanning rate; a signal regaining circuit for regaining recorded information on the basis of a detection signal supplied by the radiation-sensitive detector; a load circuit for loading the regained information in an output buffer memory at a given load rate; a signal retrieval circuit for retrieving the information stored in the buffer memory at a given retrieval rate which is lower than the load rate; control means for interrupting the storage of the regained information in the buffer memory for displacing the scanning spot after a given time interval to the track portion where loading was interrupted and for subsequently resuming the storage of the regained signal at an instant when the scanning spot reaches a track position which corresponds to the position where the loading of the buffer memory was interrupted, such that a filling level of the buffer memory remains between given limits.
The invention also relates to an optical recording device for recording information in a track of an optical record carrier, which device comprises a write unit for providing an information pattern in the track in response to a write signal, for which purpose the write unit comprise a radiation source for generating a radiation beam; an optical system for directing the radiation beam via the track onto a radiation-sensitive detector; the radiation beam producing a scanning spot on the record carrier. The device further comprises a driving device for displacing the scanning spot with respect to the record carrier in a longitudinal direction of the track at a given scanning rate; an input buffer memory for storing information to be recorded at a given load rate; a retrieval circuit for retrieving the information from the input buffer memory at a retrieval rate which is higher than the load rate; a control circuit for converting the retrieved information into the write signal; control means for interrupting the retrieval of the information from the input buffer memory, for displacing the scanning spot after a given time interval to the track portion where the retrieval was interrupted and for subsequently resuming the retrieval of the information, such that a filling level of the input buffer memory remains between given limits.
An optical reading device and an optical recording device of the type described in the opening paragraphs are known, inter alia, from EP-A-0.429.139. It is an object of the invention to provide a reading device of the type described and a recording device of the type described which have a low power consumption.
As regards the reading device, this object is achieved in that the device comprises means for switching off at least the radiation source in time intervals in which the loading of the buffer memory is interrupted.
As regards the recording device, this object is achieved in that the device comprises means for switching off the radiation source in time intervals in which the retrieval of the information is interrupted.
By switching off the radiation source during the time intervals when reading and recording are interrupted, the power consumption of the radiation source is considerably reduced. Since this power consumption constitutes a considerable part of the overall power consumption, the invention yields a considerably economy. For the purpose of illustration, it is to be noted that the power consumption of the radiation source in reading devices is approximately half the overall power consumption. Such power consumption economy is particularly advantageous when the invention is used in battery-fed devices.
Optical reading devices and recording devices are usually provided with a focusing element for focusing the radiation beam. A focal point of the radiation beam is held in, such a plane in which information is recorded. To this end the device is generally provided with a feedback focus control controlling a focus actuator on the basis of a focus error signal in such a way that a position of the focal point fixed by the control signal of a focus actuator is retained in the plane of the information layer. In the most conventional focus controls, a focus error signal is derived from the radiation beam reflected by the information layer. The focus error signal is indicative of the focus error only in a limited measuring range of the focal point. The feedback focus control can, therefore, operate in a reliable manner only when the focal point is located within this measuring range. When the reading operation is started, a capturing procedure is performed in which the focal point is brought within the measuring range. Such a capturing procedure is also performed when the focal point is outside the measuring range. By means of known capturing detection circuits, it can be ascertained whether the focal point is present within the measuring range. There is a risk that the focal point is no longer located within the desired range after the radiation source has been switched on again so that the capturing procedure must be repeated. The drawback of such a capturing procedure is that it is relatively time-consuming.